FLAP 2.2 & WaterFLAP

FLAP (Fingerprints for Ligands and Proteins) provides a common reference framework for comparing molecules, using GRID Molecular Interaction Fields (MIFs). The fingerprints are characterised by quadruplets of pharmacophoric features and can be used for ligand-ligand, ligand-receptor, and receptor-receptor comparison. In addition, the quadruplets can be used to align molecules, and a more detailed comparison of the GRID MIF overlap calculated. When the template is a ligand, this enables ligand-based virtual screening and alignment. When the template is a receptor site, this enables structure-based screening and pose prediction.
FLAP 2 includes WaterFLAP, a new approach to predicting binding site waters and using them for structure-based design. The waters are scored using two new GRID fields; the CRY field for combined hydrophobicity and lipophilicity, and the ENTR field to estimate the entropic character of a particular water molecule. Combined with the GRID OH2 water enthalpy prediction, waters can therefore be assessed as to their structural, displaceable, or bulk character.
The docking engine FLAPdock has been extensively re-parameterized and validated on hundreds of crystal structures, and now includes the ability to use the WaterFLAP waters to guide the docking.
GRID is also directly accessible to characterise binding sites in terms of their Molecular Interaction Fields to enable straightforward structure-based design.

Parallelisation of virtual screening using MPI for extra high-throughput on Beowolf clusters

Figure 1. Virtual screening enrichment analysis to select the best scoring function on a set of RXR-alpha inhibitors.

FLAPpharm is a derivative method that uses the FLAP ligand-based alignments
to derive template-independent common alignment models for a set of active
ligands. From the alignment model, the pharmacophoric interaction fields
can be calculated and used for both screening, docking, and increase
understanding of SAR. The method has been validated using an extensive pharmacophore
validation dataset consisting of 81 targets (PharmBench).

Figure 2. FLAPpharm alignment model and pharmacophoric interaction fields of a set of PARP inhibitors

Given a set of aligned active molecules, FLAP is also able to perform
3D-QSAR by statistical analysis of the GRID MIFs, to enable a detailed
examination of an active series and lead optimisation to be performed.

Figure 3. 3D-QSAR analysis for a set of PDGFR inhibitors

Within a binding site, waters are predicted and scored using WaterFLAP. The superimposed ligand is 600-fold less active due to the displacement of a key water within the site, which WaterFLAP highlights as being tightly bound and therefore not displaceable.

Figure 4. WaterFLAP water prediction for the PGDS binding site

FLAPdock enables flexible fragment-based docking, and can include optional waters from WaterFLAP to guide the docking when water mediate interactions are known to be important. The ligand poses from 4EE0 dock successfully with the WaterFLAP waters, interacting with the key structural binding site water. Docking is not successful without including the key structural water.

Figure 5. FLAPdock pose prediction of PGDS ligand from 4EE0 using WaterFLAP waters, into the structure of 4EDY.

FLAP also provides a projection of bound ligands and GRID MIFs in the context of the site as a 2D schematic representation to facilitate design and communication.